1. Field of the Invention
This invention relates generally to the field of drilling. More specifically, the invention relates to compositions and methods for annular pressure buildup mitigation.
2. Background of the Invention
Natural resources such as oil or gas residing in a subterranean formation are recovered by drilling a well into the formation. The subterranean formation is usually isolated from other formations using a technique known as well cementing. In particular, a wellbore is typically drilled down to the subterranean formation while circulating a drilling fluid through the wellbore. After the drilling is terminated, a string of pipe (e.g. drill string, casing) is run in the wellbore. Primary cementing is then usually performed where cement slurry is pumped down through the string of pipe and into the annulus between the string of pipe and the walls of the wellbore to allow the cement slurry to set into an impermeable cement column and thereby seal the annulus. Secondary cementing operations may also be performed after the primary cementing operation.
After completion of the cementing operations, production of the oil or gas may commence. The oil and gas are produced at the surface after flowing through the wellbore. As the oil and gas pass through the wellbore, heat may be passed from such fluids through the casing and into the annular space, which typically results in expansion of any fluids in the annular space.
Annular pressure build-up (APB) is a potentially dangerous condition in wells caused by a temperature driven increase in pressure within the annuli formed by downhole strings. APB situations commonly occur in subsea wells, where annuli between adjacent casing strings are sealed from above by wellhead equipment at the mudline and from below by cement tops or barite plugs. Pressure within the annuli is built up as the temperature within the annuli is increased due to the expansion of drilling fluids within the annuli. A significant increase in pressure within the annuli may have adverse consequences such as rupture of the casing wall or catastrophic collapse of the drilling string itself or of the production tubing through which wellbore fluids are brought to surface.
Several techniques for mitigating APB have already been developed and employed with some regularity in the industry. One mitigator, for example, is syntactic foam composed of hollow glass elastic hollow particles with prescribed dimensions. The foam is attached to the outside surface of the inner string of the annulus. Onset of APB above a particular pressure level causes the elastic hollow particles to collapse and break, increasing the available volume of the annulus. These and other commonly used techniques, however, are limited in utility in that they provide only a one-time relief of APB; once activated, the mitigator cannot relieve future instances of pressure buildup.
Consequently, there is a need for more effective compositions and methods for mitigating annular pressure buildup.